Elevator systems are useful for carrying passengers, cargo or both between various levels within a building, for example. There are various considerations associated with operating an elevator system. For example, there is a desire to provide efficient service to passengers. One way in which this is realized is by controlling the flight time of an elevator car as it travels between levels in a building. There are practical constraints on an elevator flight time dictated by the machinery used for moving the elevator and the desire to provide a certain level of ride quality. For example, passengers would feel uncomfortable if the elevator car accelerated or decelerated at certain rates. Therefore, ride comfort constraints are implemented to ensure that passengers have a comfortable ride.
There are competing considerations when attempting to maximize the traffic handling capacity of an elevator system (i.e., to minimize flight time) and to maximize the ride comfort of passengers. Adjusting the control parameters in one direction to decrease the flight time typically results in a decrease in ride quality. Conversely, adjusting control parameters to increase ride quality usually causes a sacrifice of efficiency in terms of flight time.
For example, an elevator control arrangement typically dictates a motion profile of the elevator car that sets limits on velocity, acceleration and jerk. When vibration levels in an elevator car are too high, the typical approach is to reduce the values of the jerk, acceleration, velocity or a combination of these. Attempting to minimize vibration and improve ride quality, however, typically increases the associated flight time. To maintain a comfortable ride, conventional wisdom has been to decrease acceleration, for example to provide improved ride quality. Unfortunately, however, decreased acceleration increases the flight time for a particular elevator run, which may prove inconvenient or inefficient in terms of performance. If the goal is to avoid an increase in flight time while decreasing acceleration in an attempt to improve passenger comfort, there typically will be an associated increase in jerk rate. Introducing higher amounts of jerk, however, results in higher amounts of vibration in the elevator car which defeats the reason for decreasing acceleration in the first place (e.g., to improve ride quality or passenger comfort).
FIG. 1 shows a typical elevator motion profile 20. A first plot 22 represents the position of the elevator car during a single run from an initial position to a selected landing at a scheduled stop. The velocity of the elevator car is shown at 24. An associated acceleration curve is shown at 26. The example of FIG. 1 includes a plot 28 showing jerk values during the elevator run. In this example, the jerk value begins at 30 and is instantaneously changed at 32 to a maximum value shown at 34. At the same time (e.g., at 32) the elevator car acceleration begins in this example. Once the acceleration reaches a constant level, the amount of jerk is instantaneously changed at 36 back down to a zero value shown at 38. As the elevator car continues to move in this example, the distance remaining to the intended landing warrants initiation of a stopping sequence. This causes the jerk to change instantaneously at 40 to the level at 42, which in turn causes the acceleration to begin to decrease. As the elevator car approaches the intended landing, the jerk rate at 42 is maintained until the acceleration rate crosses through zero value and becomes the negative of the value achieved at 36. This causes an instantaneous change in jerk at 44. As the elevator car approaches the landing, there is an instantaneous change in the jerk value at 46 back to a maximum value shown at 48 and finally an instantaneous change at 50 back down to a zero value.
As can be appreciated from FIG. 1, a typical elevator motion profile includes a generally square-wave shaped jerk profile. Setting appropriate limits on the acceleration, velocity and jerk allows for controlling the ride comfort for passengers on such an elevator run.
It would be useful to be able to control an elevator motion profile in a way that provides a desired level of ride quality without sacrificing performance by increasing flight time, for example.